High-power feed-forward microwave amplifier apparatus with out-of-band

Abstract

A replica of a microwave input signal is subtracted from an amplified version of the input signal produced by main power amplifiers (52a,52b) to produce an error signal corresponding to distortions introduced into the input signal by the power amplifiers (52a,52b). The error signal is amplified by an error amplifier (30), and subtracted from the amplified input signal to produce an output signal in which the distortions have been canceled. A bandpass filter (54) is provided immediately following the power amplifiers (52a,52b) to suppress or block intermodulation products generated in the power amplifiers (52a,52b) which are outside the bandwidth of the input signal and which could overload the error amplifier (30) to generate further distortion. A second filter (78) may be provided through which the replica signal passes to better match the replica signal to the amplified and filtered input signal. Suppression of the out-of-band intermodulation products enables operation of the power amplifiers (52a,52b) very close to their saturation limit with maximum efficiency. A second error cancellation branch (56,60,62,64,66,68,70,72) may be provided to produce further reduction of distortion, and may include a third bandpass filter (80).